Italian citizenship may be granted as a concession, known as “naturalisation”, based on one of the grounds set out in Article 9 of the 1992 citizenship law. The decision to grant citizenship on these grounds is at the discretion of the Ministero dell’Interno, who must be satisfied that the applicant is sufficiently integrated into Italian society, although there is no “test” of knowledge or language as is the case with applying for British citizenship.

EU nationals are eligible to apply for Italian citizenship after continuous residence of more than 4 years.

http://www.oliverpartners.it/italian-citizenship-rights-eu-nationals/

Non EU nationals may apply on the basis of continuous residence of at least 10 years in Italy.

Continuous lawful residence must be proved in both cases by demonstrating registration at the Anagrafe of the Comune of residence, for at least the required period. In the absence of this (for example employees of UN organisations based in Italy who are exempt from registration as resident in Italy) residence is proved by demonstrating the periods during which they held the relevant permit issued by the Ministry of Foreign Affairs or a permesso di soggiorno (non EU residents only).